Effects of Dissipation and Temperature on Macroscopic Quantum Tunneling

Measurements of the tunneling rate $\Gamma$ out of the zero-voltage state for several Nb edge junctions with differing shunt capacitances are described. At zero temperature, increasing the shunt capacitance lowers $\Gamma$ in agreement with dissipative calculations of the macroscopic-quantum-tunneling rate. As temperature increases, $\ln \left[\frac{\Gamma \mathrm{}\left(T\right)\mathrm{}}{\Gamma \mathrm{}\left(0\right)\mathrm{}}\right]\propto T^2$ as recently predicted.